1. Field of the Invention
This invention relates to an adjustable vibration damper for motor vehicles with a cylinder containing damping fluid, an axially-movable piston rod immersed therein, and a damping piston attached to the piston rod, which divides the cylinder into two work chambers, and a damping valve equipped with a valve seat, which by means of an axially movable valve body controls the effective cross section of a damping passage, whereby the valve body has at least one constant throttle cross section running from its pressurized end surface to the opposite back side, and an additional throttle passage running from the back side in the discharge direction of a flow connection is controlled by an axially movable, continuously positionable control pin.
2. Background Information
The prior art discloses hydraulically adjustable vibration dampers (e.g. DE-PS 37 19 113), corresponding to U.S. Pat. No. 4,880,086 whose damping force in the decompression and compression direction can be continuously adjusted. For this purpose, a damping valve equipped with an axially movable valve body and a valve seat controls the effective cross section of a damping passage. The throttle cross section of the damping passage is thereby controlled by an axially movable, continuously positionable control pin which interacts with the valve body. In such an arrangement, the damping valve can receive the flow on one side only, and is therefore suitable primarily for use in two-tube dampers having a bypass system. Use of such a damping valve in a single-tube vibration damper requires a complex construction with numerous check valves and thus leads to restrictions in the tuning of the damping forces in the decompression and compression stages.
The prior art also discloses adjustable vibration dampers for motor vehicles (e.g. DE-OS 34 28 306), in which there is an apparatus to influence the damping forces in the damping piston of the vibration damper. On account of the design of the valve, the adjustable apparatus in the damping piston can receive the flow from two sides. The apparatus is oriented so that between the main stage and the pilot stage, there is no displacement feedback but there is only a force feedback produced by leaf springs, so that during the equalization of the damping forces, the user must put up with problems, with imprecise force and time behavior and with a tendency to self-excited vibrations. An additional disadvantage is the complicated structure, in particular the connection of the power feed to the moving magnet coil in oil. Another disadvantage is that the effect of the electromagnetic intervention in the damping force curve reverses between the decompression and compression stage (the high decompression stage corresponds to the low compression stage and vice-versa).